1. Field of the Invention
This invention relates in general to monitoring downhole pressures in a well, and in particular to a system for monitoring both intake and discharge pressure of a centrifugal pump.
2. Description of the Prior Art
In a submersible pump well system, a downhole electric motor rotates a centrifugal pump. The pump is connected to tubing for pumping the well fluid drawn in from the annulus surrounding the tubing to the surface.
In some systems, the intake pressure to the pump is monitored. The intake pressure is important to determine well drawdown and the response of the reservoir at various flow rates. The intake pressure is monitored by a downhole pressure sensor. The signal from the pressure sensor is monitored at the surface either through a separate line or by superimposing the signal onto the power cables used to supply power to the motor. Temperature is also measured in some installations.
One disadvantage of the present systems is that they do not have any means for also monitoring the downhole discharge pressure of the pump. Consequently, the true differential pressure of the pumping system cannot be obtained. The true differential pressure of the pump is important for determining the pump operating point on the flow-head curve. This is valuable for pinpointing pump performance and pumping problems.
Another disadvantage with some of the present systems is that the downhole pressure sensing equipment cannot be retrieved without pulling the tubing and the pump. Pulling the tubing and the pump is an expensive operation, and is normally performed no more than about every eighteen months for purposes of repairing a failed pumping system. As a result, if the pressure sensor malfunctions, normally, the operator must wait until it is time to pull the pump before repairing or replacing the pressure sensor. Several months may pass where the well would be without any type of pressure sensor.